How to fix Error 1957 on Windows Server 2025 / Windows 11

by

Troubleshooting Guide: SQL Server Error 1957 – Imprecise User-Defined Function in Indexed View

Why This Error Happens

This error occurs because SQL Server requires all functions referenced in an indexed (schema-bound) view to be marked as precise (deterministic and non-imprecise) so that the query optimizer can reliably maintain the index. A scalar or table-valued user-defined function (UDF) is considered “imprecise” if it contains floating-point operations (like float or real data types) or non-deterministic logic that SQL Server cannot guarantee will return the same result given the same inputs. Since indexed views physically materialize data, SQL Server blocks the CREATE INDEX operation to prevent data integrity issues caused by inconsistent function results.

Step-by-Step Resolution Guide

Step 1: Identify the Offending Function

  • Open SQL Server Management Studio (SSMS) and locate the specific view mentioned in the error message (the %.*ls placeholder).
  • Run the following query to check the function’s properties:
  • SELECT OBJECTPROPERTY(OBJECT_ID('YourFunctionName'), 'IsDeterministic') AS IsDeterministic;
  • A return value of 0 confirms the function is non-deterministic or imprecise.

Step 2: Refactor the Function to Remove Floating-Point Types

  • Edit the T-SQL definition of the user-defined function.
  • Replace any FLOAT or REAL data type declarations within the function’s logic and return type with precise numeric types such as DECIMAL(18, 4) or NUMERIC.
  • Ensure the function does not call other non-deterministic system functions (e.g., GETDATE(), NEWID(), or RAND()) if precision is required for the index.

Step 3: Apply the WITH SCHEMABINDING Option

  • Alter the function using the ALTER FUNCTION statement to include the WITH SCHEMABINDING clause. This forces SQL Server to re-evaluate the function’s determinism and locks the schema of underlying objects.
  • Example syntax:
  • ALTER FUNCTION dbo.YourFunctionName() RETURNS DECIMAL(18,2) WITH SCHEMABINDING AS BEGIN ... END

Step 4: Remove the Reference as a Workaround

  • If altering the function is not feasible due to third-party dependencies, modify the view definition to remove the call to the imprecise function entirely.
  • Replace the function logic directly within the view using inline precise T-SQL calculations instead of a function call.

Step 5: Re-attempt the Index Creation

  • Navigate back to the view in SSMS Object Explorer.
  • Run the CREATE UNIQUE CLUSTERED INDEX command again on the view to verify the schema-binding restrictions have been satisfied.

Alternative or Verification Steps

  • Verification: Run SELECT OBJECTPROPERTY(OBJECT_ID('dbo.YourFunction'), 'IsPrecise') in a query window; a result of 1 confirms the fix was successful before re-indexing.
  • Alternative: If the function must remain imprecise for business logic reasons, abandon the indexed view strategy for this specific view and rely on standard non-clustered indexes on the underlying base tables instead to improve query performance.